1. Field of the Invention
The invention relates to an active sound reproducer. This is understood to mean a sound reproducer which receives an unprocessed audio signal and subjects this signal to signal processing operations such as tone control and power amplification. The invention also relates to a control unit for controlling such a sound reproducer.
2. Description of the Related Art
An active sound reproducer of the type described in the opening paragraph is known from European Patent Application EP-A1-0 082 905. This known active sound reproducer has an audio input for receiving the audio signal, a signal processing circuit for processing the audio signal in response to supplied setting signals, a control input for receiving the setting signals and a control circuit for applying the setting signals to the signal processing circuit. An audio signal which is still unprocessed is applied to the sound reproducer. The term unprocessed is understood to mean that the signal has not yet undergone any processing operations such as volume, tone and balance control. The audio signal is not subjected to signal processing operations until it has reached the sound reproducer. The control signals required for this purpose are referred to as setting signals. They comprise, inter alia, the desired volume, tone and balance values and are also applied to the sound reproducer.
The known sound reproducer receives the audio signal and the setting signals from a transmitter section which will hereinafter be referred to as control unit. The control unit selects the audio signal to be reproduced from a plurality of sound sources and applies this signal to the sound reproducer. Moreover, the control unit generates the setting signals in response to remote control commands which are received from a remote control unit. Sound sources are, for example, a record player, a tuner, a cassette player, a CD player etc. The audio signal and the setting signals are digitally transmitted to the known sound reproducer. Where necessary, the audio signal from the sound source is digitized by the control unit and formatted for transmission.
It will be evident that digitization is not necessary if the sound source already generates a digital signal. It is even feasible that a given sound source, for example, a CD player, already generates a digital audio signal itself in a format which is suitable for direct supply to one or more sound reproducers. In principle, an expensive control unit is superfluous in that case. Existing sound sources such as CD players are, however, not adapted to generate the setting signals for the sound reproducer and to apply these signals to the speakers. Consequently, the known sound reproducers cannot be directly connected to a CD player. The same problem occurs if there is a control unit which is not adapted to apply the setting signals to the sound reproducers. This may occur if the control unit and the sound reproducers are not compatible, for example, because they are of different brands.
The transmission of an unprocessed audio signal and the associated setting signals to active sound reproducers has the advantage that the same audio signal, but different setting values can be applied to different sound reproducers. Said European Patent Application states that different carrier frequencies can be used for this purpose for different sound reproducers, or that the setting signals can be transmitted in time-division multiplex for a plurality of sound reproducers. It is possible, for example, to arrange a sound reproducer (or a set of sound reproducers in the case of stereo reproduction) in the living room and to arrange another sound reproducer in another space, for example, a bedroom. The same audio signal is applied to the two sound reproducers. Since the sound reproducers are implemented as active speakers and receive different setting signals, volume, tone and balance are separately adjustable in both spaces. However, the user operates the known sound reproducers in the space where the control unit is located. When the control unit is located in the living room, it is then impossible, for example, to control the sound volume in the bedroom.